1. Field of the Invention
The present invention relates generally to a mobile communication system, a communication control method, a base station and a mobile station to be used in the same. More particularly, the invention relates to a mobile communication system, a communication control method, a base station and a mobile station to be used in the same suitable for use in High Speed Downlink Packet Access (HSDPA) system for high speed data transmission in downlink from the base station to the mobile station.
2. Description of the Related Art
Study has been made for a high speed downlink packet access (HSDPA) system of this kind in Third Generation Partnership Project (3GPP). In the HSDPA system, a High Speed-Physical Downlink Shared Channel (HS-PDSCH) is used for downlink (DL) transmission from the base station to the mobile station. The HS-PDSCH is adapted for data transmission. One HS-PDSCH is shared by a plurality of mobile stations by sharing in time (time sharing).
In the HSDPA system, for controlling data transmission from the base station to the mobile station, an uplink Dedicated Physical Control Channel (DPCH) and an uplink High Speed-Dedicated Physical Control Channel (HS-DPCCH) are set between the base station and a plurality of mobile stations, respectively. The uplink (UL) DPCH is used for transmitting a control information, such as data transmission timing information and so forth from the mobile station to the base station On the other hand, UL HS-DPCCH is used for transmission of Acknowledge/Negative Acknowledge (ACK/NACK) information of Hybrid-Automatic Repeat request (HARQ) (meaning of which will be discussed later) and quality information to the base station by the mobile station.
Here, quality means a quality (Ec/Io: [energy per chip/interference wave power per unit frequency]) of a Common Pilot Channel (CPICH) signal.
However, in the conventional such HSDPA system, in order to continue setting of UL DPCH and UL HS-DPCCH after initiation of setting of the HS-PDSCH, a large number of mobile stations which are unnecessary to transmit quality information, namely a large number of mobile station not performing packet reception set HS-DPCCH to make UL interference power significant. Furthermore, a capacity of uplink radio channel is significantly limited.
Furthermore, since the mobile station continuously transmit the quality information, power consumption becomes significant to shorten operation period of a battery. Also, since the base station performs transmission of the quality information at a predetermined timing and a predetermined interval, the base station cannot receive the quality information at the timing transmitting data to the mobile station.